The present invention was made as the result of work under a contract with the Federal Highway Administration of the United States of America, Contract No. DTFH61-81 C 00076.
Guardrails are traffic barriers placed along the roadside to screen errant vehicles from hazards behind the barrier. The most common guardrail in the U.S. is constructed using the standard steel W-beam mounted on spaced wood or steel posts. Because the W-beam functions primarily in tension when redirecting impacting vehicles, a function of the end is to provide necessary anchorage for the beam to develop necessary tensile forces. In addition, since the guardrail end represents a discontinuity in the barrier system, it is subject to being struck "head-on" by vehicles with small departure angales from the roadway. These head-on impacts have proved to be troublesome with W-beam barriers because of the significant spearing strength of the beam element. Some widely used terminal designs "bury" the W-beam at the end to eliminate spearing, but this design has been shown to cause vaulting and rollover due to the vehicle riding up the end, and subsequently becoming airborne.
Highway agencies have been using crash cushion devices at high accident locations for a number of years. These devices, costing from $5,000 to $20,000, absorb the energy of head-on impacts with decelerations that are not life-threatening for design conditions. Because the number of guardrail terminals is quite large, and the impact probability low for most, the states do not have the resources to employ crash cushion devices at most guardrail ends.
Development of terminal designs is complicated by the need to minimize end-on resistance for the small car impacts while still providing the necessary strength for full-size car impacts either on the end or downstream of the approach end.
The present invention is directed to an energy absorbing guardrail terminal which functions essentially as a crash cushion by providing a series of spaced openings which are in line with the spliced bolts when two beams are overlapped. This provides an energy absorbing mechanism as the rails are telescoped relative to each other by the spliced bolts shredding out the metal strips between the openings. The shredding of the material provides a uniform and controlled energy absorption mechanism. In addition, the sections of the guardrails are staged so that the upstream section will telescope first so as to minimize end-on resistance for the small car impacts while still providing the strength necessary to absorb full-size car impacts.